Modal analysis of the LEGO® plate

It’s important for the isolation purpose to know how the system moves and which its Eigen frequencies (natural frequencies) are.

In order to get this information a modal analysis is carried out. With a shaker the LEGO® structure is exited in a point and the velocity of 66 points is taken.

This measurement is done by a Laser-vibrometer.

The structure is subspended during the measurements in order to try to eliminate or reduce undesired and unmeasured exitatiuons that could give rise to unreliable results.

From the results obtained the suggestion is that the LEGO® structure acts as a linear structure (a uniform plate) until 400 Hz at least. So is possible to reconstruct the behavior of the plate with the classical theory.

In the figure below the experimental (blue) and reconstructed (red) Frequency Response Functions are reposted for the co-located point that is one of the corners of the plate. This point is chosen because it’s the point in which the actuator for the isolation purpose will be placed.

A good reconstruction of the behavior of the structure is achieved.

It is now possible to visualize the modes of the structure. One of the tool of the Laser-vibrometer let us to visualize directly the mode shapes, so it’s now possible to compare the reconstructed behavior(right side) with the “experimental” one (left side).

For simplicity only the first three Eigen modes that correspond to the first three Eigen frequencies (first three peaks) are reported.

It is possible to see that the linear reconstruction of the system is a good approximation and gives good results.

Now the reconstructed behavior will be used to build a control for the vibration isolation purpose.

See you soon.